1. Field of the Invention
This invention relates to cooling apparatus suitable for cooling a fluid passing therethrough, particularly a molten metal, for example, molten magnesium.
2. Description of Prior Art
A hot fluid can be cooled to a lower temperature level by passing the same through one or more metal tubes whose outer walls are maintained at a temperature below the temperature of said hot fluid by contacting said outer walls with a cooler fluid whose temperature is appreciably below the temperature of said hot fluid. It is apparent that in many cases it is desirable, and sometimes critical, to make certain that there is no contact during such cooling between the hot fluid and the cooling fluid. For example, when the cooling fluid is chemically different from the hot fluid being cooled, mixture of the two would result in contamination of the hot fluid with the cooling fluid, resulting in purification steps that might not be economically feasible. If the hot fluid being cooled is composed of molten metal, for example, molten magnesium, and the cooling fluid is a normal cooling liquid, such as water, contact between the two could lead to disastrous results.
Cooling apparatus can be designed that, for a period of time, will reasonably avoid the contact of the hot fluid with the cooling fluid. For example, the tube through which the hot fluid will pass can be inserted inside a second tube, wherein the outer surface of the inner tube is in intimate contact with the inner surface of said second tube. Since the surfaces of the two tubes are thus in intimate contact with each other, it would be expected that heat transfer between the walls of the two tubes would not be adversely affected thereby. But even more important, failure by way of a crack or an opening in one wall of one of the two tubes would still not result in intermixture of the hot fluid with the cooling fluid.
However, to insure that at some point a similar failure does not occur in the wall of the remaining tube, periodic inspections of the tubes, or the replacement thereof, becomes necessary. Replacement of the tubes is obviously expensive. Inspection of each tube, when they have been assembled, as described above, so that the surfaces thereof are in intimate contact with each other, is very difficult or virtually impossible. This is so, because when they are assembled, they must be prestressed. This is done by heating the outer tube while cooling the inner tube and then inserting one tube inside the other while they are in such state. When the two tubes reach ambient temperature, the inner tube will fit snugly within the outer tube. Separation of the tubes from each other thereafter cannot be done easily and in some cases will be virtually impossible. This means that the inner surface of the outer tube and the outer surface of the inner tube cannot effectively be examined and inner surface of the inner tube may be examined but with great difficulty. Therefore, in situations wherein the cooling apparatus has been designed, as defined above, the same cannot effectively be inspected and will have to be periodically replaced, with added expenses.